In a polymer actuator, the thickness and uniformity of a conductive polymer film are desirably controlled accurately, because they affect the response speed and displacement ratio of the actuator. A conductive polymer film is generally produced by an electrochemical polymerization method, which comprises immersing a working electrode and a counter electrode in a monomer solution, and supplying electric current between both electrodes. Although the thickness of the resultant conductive polymer film would be able to be accurately measured by an atomic force microscope if it were taken out of the solution, it would need lengthy steps.
To accurately control the thickness of a conductive polymer film, it is desirable to measure the change of the thickness with time while forming the film. Although the production of a conductive polymer film by a gas-phase reaction while irradiating infrared rays makes it possible to detect the change of thickness with time by a reflection-type infrared thickness meter, the production of a conductive polymer film by an electrochemical polymerization method does not make the measurement of the thickness using a reflection-type infrared thickness meter possible, because the solution hinders the measurement.
A conductive polymer film used for a polymer actuator, etc. is desirably uniform not only in a planar direction but also in a thickness direction, such that it can show stable performance. Even a largely extendable, conductive polymer film would not be useful for practical applications because of lack of reliability, if it were not uniform in a thickness direction. To make the electrochemically polymerized conductive film uniform in a thickness direction, it is desirable to have a constant film-forming speed. However, a constant-voltage or current method generally used in the electrochemical polymerization method fails to provide a constant film-forming speed. In the case of the constant-voltage method, electric resistance at an interface between the electrode surface and the solution changes as the film grows. Accordingly, even if a constant voltage were applied, the voltage actually applied to the film would not be constant, failing to achieve a constant film-forming speed. In the case of the constant-current method, the film surface roughness changes as the film grows, resulting in the change of current per a unit area, and thus the change of the film-forming speed. In any method, a constant film-forming speed cannot be achieved, failing to obtain a film uniform in the thickness direction.
Akao, et al., “Analysis of Formation of Conductive Polymer Film by Micro-Infrared ATR Method,” pp. 57-58, 1995, Resume of Lectures at the Tokyo Conference on Analysis Equipment And Systems, describe a system of measuring a film formed by an electrochemical polymerization method with an attenuated total reflection (ATR) prism in a micro-infrared spectrometer as an electrode. An ATR prism made of germanium as a working electrode, and a gold electrode as a counter electrode are immersed in a pyrrole solution, and voltage is applied between both electrodes to form a polypyrrole film on the ATR prism surface. The absorption spectrum of infrared rays reflected by the film via the ATR prism has a peak assigned to polypyrrole. However, a method of forming a uniform film with a constant speed has not been known.
Conductive polymer films with optimum degrees of oxidation are desired in applications other than polymer actuators, because the degree of oxidation affects the conductivity of the conductive polymer films. However, no method of controlling the degree of oxidation of a conductive polymer film has been known. A G Rangamani, et al., “Synthetic Metals,” Vol. 64, pp. 91-95, 1994 describe that with a silicon prism as a working electrode and a platinum electrode immersed in an electrolytic solution, a conductive polymer film is irradiated with infrared rays via the prism to examine its degree of oxidation. However, they have not controlled the degree of oxidation of the conductive polymer film during its formation on a real-time basis.